If this is your first visit, be sure to
check out the FAQ by clicking the
link above. You may have to register
before you can post: click the register link above to proceed. To start viewing messages,
select the forum that you want to visit from the selection below.

Announcement

Collapse

Forum Issues Update

We are continuing to work diligently to resolve the issues currently being experienced with the PhotoPlog. Thank you for your patience!

Insulation recommendations

Howdy folks, just finished up my 42" oven, standard build, and I have 3 rolls of 1" blanket for insulation of dome. Have a couple of questions please:

1. Do I just insulate the dome, or do I include the arch, inner and up to outer area?

2. I saw a post by a FB Moderator that stated FB recommends either blanket or vermiculate, not both. My intent was to use 3 layers of blanket, then cover this with vermiculite/concrete as in manual, is this the correct way?

3. Anyone who built a 42" remember how much vermiculite and concrete they purchased, and what worked for them in regards to proper mixing, and applying the product to the dome already covered with blanket?

Comment

I covered my blanket with vermiculite /portland mix - I think it was 5 to 1 (I purchased no more than three bags for the entire build). I built a cage with re-bar and chicken wire. I don't have a link to the exact page but if you slog through my build you can see the evolution (start some where in the middle). If I have time in the A.M. I will try and give you the correct page.

Comment

thanks gents, should have clarified that i my intent is to keep the dome like yours Les, not framed in, we have a pond behind and dont want to hinder view any more than possible. do you have any trouble with water, how do you keep the stucco water proofed?

Comment

If you are covering the dome with vermicrete and you make it a lean brew (10:1) it is very light and does not compress the blanket. By volume use 10:1:3 vermiculite, cement, water.
By adding the vermicrete over the blanket you can get the form back to a true hemisphere, where it was left somewhat lumpy with all the bumps and folds in the blanket.

Comment

thanks gents, should have clarified that i my intent is to keep the dome like yours Les, not framed in, we have a pond behind and dont want to hinder view any more than possible. do you have any trouble with water, how do you keep the stucco water proofed?

No trouble with water at all. I am noticing a little chipping at the base caused by freezing. A little touch up and all will be good. I used a product made by Dryvit - it's acrylic based and does a great job of repelling water.

Comment

Hi Pat
I'm at about the same point as you, a little behind, but have the same question. I've always wanted to keep the dome shape - it was always about building a round thing out of square things, after all!
So, we wrap with blanket (1" seems thin to me - not sure what thicknesses I will be able to get yet), then cover with a very light mix of vermicrete, then I had planned to render the outside with something waterproof. My neighbour is a very skilled plasterer who will help me make the last layer look professional.
Is this the sort of approach you also had in mind?

Comment

Thanks Les - that makes sense. So if my dome has a surface area of say, 2.73 sq m, allow for 3-4 times that in blanket. And allow for the chimney support up to the outer arch, I'm assuming, too.
Cheers

Comment

Thanks Les - that makes sense. So if my dome has a surface area of say, 2.73 sq m, allow for 3-4 times that in blanket. And allow for the chimney support up to the outer arch, I'm assuming, too.
Cheers

JT

JT - that would be a good amount of insulation. In regard to the chimney and outer arch - probably not required. The heat at that point is wasted so let it go? I insulated my flue because I went with type S mortar for my decorative brick - and the insulation was no more than an inch thick.

Comment

I used a 1 inch blanket to insulate the dome, which was in a double layer across most of the oven. This was then covered with approx 4 inches of 9:1 vermicrete. The blanket was held in place with chicken wire, which was tightened up by twisting the mesh with pliers. The insulation only covered the entry where there was an overlap, I did not apply any insulation specifically to insulate the brick work of that area. There is a heat break between my done and the entry to prevent heat loss through that route.

See pics below.

The vermicrete does not compress the blanket to any great extent, as it is very light.

Comment

Hi JT, yes, going same route as you, keeping it an igloo, good to hear you have a friend to help with stucco, never did that before, hope it goes ok. Started 3 curing fire all good so far, have fun with your build. Take care, pat

it's the flake variety. I'm assuming it's not going to work very well for the dome?

2. How thick do we need to go assuming this is just for covering the blanket not for insulation? I'm planning on 10:1 but we've run out of room on our dome and it's now pretty much flush with the base on the outside. The thinner at this point the better just because we have no where to go!

3. In relationship to the previous question, any idea how much portland and vermiculite we'll need for what is now about a 50" diameter?

Comment

1. Don't know what the stuff is like without seeing it, but I find 50/50 vermiculite, perlite works better than either of them alone so you could get some perlite from nursery supplies and mix it. Expect around 25% loss in volume on mixing.
2. If you only need it to get the shape nice and even you can probably get away with making it only about an inch thick but then make the brew a bit richer (say 7:1) if you tap it with the face of a trowel you can get the form remarkably even.
3. Calculate the volume required 4/3 x 3.142 x radius cubed (divide by two because it's a hemisphere) and remember you'll lose some volume on mixing.